Centrifugal pump with inner and outer casings

Abstract

A centrifugal pump with an outer casing which has one or more discharge branches, with an inner casing which is installed in the outer casing and rotatably surrounds a pump shaft, and an impeller which is mounted on the shaft at the inlet of the outer casing has one or more fluid flow guiding inserts, one for each discharge branch, in an annular chamber between the inner and outer casings. The inserts are offset relative to the respective discharge branches in the direction of rotation of the shaft and have front faces provided on spur-shaped front portions immediately behind the exit end of the impeller. The inserts further have guide surfaces including first sections adjacent the inner casing, second sections adjacent the outer casing, and third sections which direct a portion of the fluid medium directly from the exit end of the impeller to the corresponding discharge branches. The guide surfaces establish for the fluid medium a path which resembles that defined by the thread on a shank forming part of a screw and having a diameter which increases in a direction from the exit end of the impeller toward the discharge branches of the other casing.

We claim: 
     
       1. A centrifugal pump comprising an outer casing having a fluid-admitting inlet and an outlet including at least one lateral fluid discharge branch; an inner casing disposed in and defining with said outer casing a chamber connecting said inlet with said outlet; a pump shaft rotatably journalled in said inner casing; an impeller mounted on said shaft between said inlet and said chamber for rotation in a predetermined direction; and fluid flow controlling guide means including at least one insert in said chamber, said inner casing having an outer diameter which increases from said impeller toward said outlet and said insert having a front face adjacent said impeller and a guide surface adjacent said casings, said front face being offset relative to the center of said at least one discharge branch in said predetermined direction and said guide surface including a first section nearer to said inner casing and a second section nearer to said outer casing, said first and second sections extending from said front face in said predetermined direction and said guide surface further including a third section which extends counter to said direction and is nearer to said at least one discharge branch than said first and second sections. 
     
     
       2. The pump of claim 1, wherein said outlet includes a plurality of lateral discharge branches and said guide means comprises one insert for each of said discharge branches. 
     
     
       3. The pump of claim 1, wherein said third section is steeper than said first and second sections. 
     
     
       4. The pump of claim 1, wherein said guide surface is stepped and each of said first and second sections constitutes a step of said guide surface. 
     
     
       5. The pump of claim 1, wherein said first section is more distant from and said second section is nearer to said impeller in the axial direction of said shaft. 
     
     
       6. The pump of claim 1, wherein said at least one discharge branch extends substantially radially of said shaft and said outer casing includes a substantially funnel-shaped portion disposed between said chamber and said at least one discharge branch and tapering toward said at least one discharge branch. 
     
     
       7. The pump of claim 1, wherein said outer casing has at least one internal recess disposed between said chamber and said at least one discharge branch and extending circumferentially of said at least one discharge branch. 
     
     
       8. The pump of claim 1, wherein said at least one discharge branch has a predetermined width in the direction of fluid flow from said inlet to said at least one discharge branch, said front face being offset by a distance which at most matches said width. 
     
     
       9. The pump of claim 1, wherein said at least one insert is a discrete part which is insertable into and removable from said chamber. 
     
     
       10. The pump of claim 1, wherein said at least one insert is an integral part of said outer casing. 
     
     
       11. The pump of claim 1, wherein said at least one insert is an integral part of said inner casing. 
     
     
       12. The pump of claim 1, wherein at least one of said casings is a casting. 
     
     
       13. The pump of claim 1, wherein said at least one insert is a casting. 
     
     
       14. The pump of claim 1, wherein said impeller is an axial impeller. 
     
     
       15. The pump of claim 1, wherein said impeller is a mixed flow impeller. 
     
     
       16. The pump of claim 1, wherein said impeller is open.